In packet communication systems, packet retransmission is often requested when a received packet is detected to be in error. This scheme, termed automatic retransmission request (ARQ), is intended to reduce packet errors. However, retransmitting the same information several times tends to reduce the communication system throughput. To reduce the number of required retransmissions, more efficient ARQ techniques are typically used.
Hybrid ARQ (H-ARQ) techniques, which include Chase combining and incremental redundancy, have been shown to improve efficiency by reducing ARQ overhead. H-ARQ techniques are primarily designed assuming a single-antenna transmitter and receiver. In standard proposals submitted to HSDPA and 1xEVDV, symbol/bit combining (i.e., Chase combining) or incremental redundancy has been used in the H-ARQ technique. Transmit Diversity (TD) has been used in the IS-2000 and Wideband Code Division Multiple Access (WCDMA) standards and in their current evolution proposals. In the IS-2000 standard, for example, two open loop TD schemes have been adopted, i.e., Orthogonal Transmit Diversity (OTD) and Space-Time Spreading (STS). In WCDMA, both open and closed loop TD schemes have been adopted.
The use of multiple antennas to increase system throughput/data rate has started to gain attention in some communication systems, such as in third generation wireless systems like the 3GPP (3rd Generation Partnership Project) and 3GPP2 standards bodies. Different multi-antenna techniques have been proposed for those standards, such as the use of transmit diversity and multi-input multi-output (MIMO) antenna processing techniques. Although the above-mentioned techniques serve their intended purpose, a need exists in the art for HARQ techniques that fully exploit the characteristics of MIMO channels by providing for improved data throughput and system capacity.